1. Technical Field of the Disclosure
The present invention relates to an apparatus and method for bending a glass tube to a U shape, and more particularly to an improvement of an apparatus for bending a glass tube to a U shape by using a bending drum. The glass tube may be used for a bulb of U-shaped fluorescent lamps and may have other uses.
2. Description of the Prior Art
A conventional type of apparatus to obtain bulbs for U-shaped fluorescent lamps operates to heat and soften a straight glass tube at a predetermined zone for bending and then to bend the predetermined zone along a circular bending drum with the periphery formed in a groove which is semicircular in section to thus bend the glass tube to a U shape. According to such apparatus, however, the bending drum must be removed from the bent zone of the tube after the tube is bent at the predetermined zone, but since the bent zone is kept wound on the bending drum, the bending drum cannot be taken off unless it is constituted, for example, as a split-type drum. These circumstances have led to inconveniences and to a complicated bending drum structure which, in turn, inevitably requires a complicated mechanism for removing the bending drum from the bent tube. To eliminate such inconveniences, there has been developed a mechanism which will remove the bending drum immediately before the bending process at the predetermined zone for bending comes to completion, i.e., before the predetermined bending zone of the tube is completely wound on the bending drum. However, unsteadiness may result in the bending process after the bending drum is taken off, and this creates a situation where the glass tube cannot be bent accurately to a suitable U shape.